Polymeric ophthalmic lenses have become increasingly popular recently due to their fine optical properties, dimensional stability, impact resistance, and light weight. Common lens-forming materials include CR-39 (diethyleneglycol bisallyl carbonate), bisphenol A polycarbonate (PC), and poly(methylmethacrylate) (PMMA). Despite the above noted benefits to polymeric lenses, one serious drawback to polymeric ophthalmic lenses has been their susceptibility to scratching, particularly compared to traditional glass lenses.
Consequently, plastic lens surfaces have required treatment to provide a scratch- and/or abrasion-resistant layer on the lens surface to increase the field durability of the lens and retard the development of haze. Consequently, nearly all polymeric lenses have some type of scratch resistant coating. Further, additional coating layers and steps may be required in connection with the scratch resistant coating. Both front and back coatings can be applied in different ways such as dip coating or spin coating. Multiple coatings may also be necessary to obtain other desirable properties such as a mirror coating, and stain and smudge resistance.
In this regard, much research has been devoted to providing coatings for polymeric lenses to improve their abrasion resistance. In one coating method, coatings are applied sequentially in a multi-step process with a finish hard coat layer. As with many of the other coating processes, conventionally cured hard coat finishes also have several drawbacks. In general, some of the coating materials require that a primer be applied separately. While thermal cured hard coatings provide superior scratch resistance, they also require long cure times and high energy consumption for solvent evaporation. UV hard coatings provide fast cure, huge energy savings and high throughput production. However, the scratch resistance is generally poorer than that with thermal cure hard coatings.
Still further, all of the above noted coatings are susceptible to dirt collection and smudging. The surface can be cleaned by wiping with a surfactant-treated cloth or paper tissue, but the cleaning is temporary and the surface will become smudged in a short period of time, requiring repeated cleaning. Until recently, there are primarily two general methods of providing anti-fouling, anti-fingerprint, and easy cleaning features. One type is a surface treatment in the form of an over coating via a two-step process. The other type is UV curable or UV/thermal curable coating via polyfunctional acrylates. The disadvantage of the two-step surface treatment is that it is expensive and is difficult to use for high volume production, especially, for disposable protective articles. The shortcoming of a UV curable or UV/thermal curable coating via polyfunctional acrylates is that it results in relatively poor abrasion resistance as compared to the superior thermal curable polysiloxane/polyurethane based coating.
Accordingly, it is desirable to provide ophthalmic lenses offering easy cleaning features and that have superior abrasion resistance. In addition, it is desirable to provide ophthalmic lens coating compositions that impart to ophthalmic lenses resistance to dirt collection, smudging, and abrasion, cost effectiveness, long lives and suitableness for high volume production. It is also desirable to provide a method for manufacturing ophthalmic lenses that have abrasion resistance and hydrophobic properties, the method being a one-step application process that thermally cures the overlying coating composition. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.